feat: support struct/slice destructuring

Author: calebcartwright

src/formatting/expr.rs

@@ -106,11 +106,11 @@ pub(crate) fn format_expr(
             })
         }
         ast::ExprKind::Unary(op, ref subexpr) => rewrite_unary_op(context, op, subexpr, shape),
-        ast::ExprKind::Struct(ref path, ref fields, ref base) => rewrite_struct_lit(
+        ast::ExprKind::Struct(ref path, ref fields, ref struct_rest) => rewrite_struct_lit(
             context,
             path,
             fields,
-            base.as_ref().map(|e| &**e),
+            struct_rest,
             &expr.attrs,
             expr.span,
             shape,
@@ -1589,19 +1589,15 @@ fn rewrite_index(
     }
 }
 
-fn struct_lit_can_be_aligned(fields: &[ast::Field], base: Option<&ast::Expr>) -> bool {
-    if base.is_some() {
-        return false;
-    }
-
-    fields.iter().all(|field| !field.is_shorthand)
+fn struct_lit_can_be_aligned(fields: &[ast::Field], has_base: bool) -> bool {
+    !has_base && fields.iter().all(|field| !field.is_shorthand)
 }
 
 fn rewrite_struct_lit<'a>(
     context: &RewriteContext<'_>,
     path: &ast::Path,
     fields: &'a [ast::Field],
-    base: Option<&'a ast::Expr>,
+    struct_rest: &ast::StructRest,
     attrs: &[ast::Attribute],
     span: Span,
     shape: Shape,
@@ -1611,22 +1607,29 @@ fn rewrite_struct_lit<'a>(
     enum StructLitField<'a> {
         Regular(&'a ast::Field),
         Base(&'a ast::Expr),
+        Rest(&'a Span),
     }
 
     // 2 = " {".len()
     let path_shape = shape.sub_width(2)?;
     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
 
-    if fields.is_empty() && base.is_none() {
-        return Some(format!("{} {{}}", path_str));
-    }
+
+    let has_base = match struct_rest {
+        ast::StructRest::None if fields.is_empty() => return Some(format!("{} {{}}", path_str)),
+        ast::StructRest::Rest(_) if fields.is_empty() => {
+            return Some(format!("{} {{ .. }}", path_str));
+        }
+        ast::StructRest::Base(_) => true,
+        _ => false,
+    };
 
     // Foo { a: Foo } - indent is +3, width is -5.
     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
 
     let one_line_width = h_shape.map_or(0, |shape| shape.width);
     let body_lo = context.snippet_provider.span_after(span, "{");
-    let fields_str = if struct_lit_can_be_aligned(fields, base)
+    let fields_str = if struct_lit_can_be_aligned(fields, has_base)
         && context.config.struct_field_align_threshold() > 0
     {
         rewrite_with_alignment(
@@ -1637,10 +1640,14 @@ fn rewrite_struct_lit<'a>(
             one_line_width,
         )?
     } else {
-        let field_iter = fields
-            .iter()
-            .map(StructLitField::Regular)
-            .chain(base.into_iter().map(StructLitField::Base));
+        let field_iter = fields.iter().map(StructLitField::Regular).chain(
+            match struct_rest {
+                ast::StructRest::Base(expr) => Some(StructLitField::Base(&**expr)),
+                ast::StructRest::Rest(span) => Some(StructLitField::Rest(span)),
+                ast::StructRest::None => None,
+            }
+            .into_iter(),
+        );
 
         let span_lo = |item: &StructLitField<'_>| match *item {
             StructLitField::Regular(field) => field.span().lo(),
@@ -1650,10 +1657,12 @@ fn rewrite_struct_lit<'a>(
                 let pos = snippet.find_uncommented("..").unwrap();
                 last_field_hi + BytePos(pos as u32)
             }
+            StructLitField::Rest(span) => span.lo(),
         };
         let span_hi = |item: &StructLitField<'_>| match *item {
             StructLitField::Regular(field) => field.span().hi(),
             StructLitField::Base(expr) => expr.span.hi(),
+            StructLitField::Rest(span) => span.hi(),
         };
         let rewrite = |item: &StructLitField<'_>| match *item {
             StructLitField::Regular(field) => {
@@ -1665,6 +1674,7 @@ fn rewrite_struct_lit<'a>(
                 expr.rewrite(context, v_shape.offset_left(2)?)
                     .map(|s| format!("..{}", s))
             }
+            StructLitField::Rest(_) => Some("..".to_owned()),
         };
 
         let items = itemize_list(
@@ -1691,7 +1701,7 @@ fn rewrite_struct_lit<'a>(
             nested_shape,
             tactic,
             context,
-            force_no_trailing_comma || base.is_some() || !context.use_block_indent(),
+            force_no_trailing_comma || has_base || !context.use_block_indent(),
         );
 
         write_list(&item_vec, &fmt)?

tests/source/structs.rs

@@ -15,6 +15,17 @@ pub struct Foo {
     pub i: TypeForPublicField
 }
 
+// Destructuring
+fn foo() {
+    S { x: 5,
+        ..};
+        Struct {..} = Struct { a: 1, b: 4 };
+        Struct {      a,     .. } = Struct { a: 1, b: 2, c: 3};
+        TupleStruct(a,..,   b) = TupleStruct(1, 2);
+        TupleStruct(  ..) = TupleStruct(3, 4);
+        TupleStruct(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa, .., bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb) = TupleStruct(1, 2);
+}
+
 // #1095
 struct S<T: /* comment */> {
     t: T,

tests/target/structs.rs

@@ -15,6 +15,20 @@ pub struct Foo {
     pub i: TypeForPublicField,
 }
 
+// Destructuring
+fn foo() {
+    S { x: 5, .. };
+    Struct { .. } = Struct { a: 1, b: 4 };
+    Struct { a, .. } = Struct { a: 1, b: 2, c: 3 };
+    TupleStruct(a, .., b) = TupleStruct(1, 2);
+    TupleStruct(..) = TupleStruct(3, 4);
+    TupleStruct(
+        aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa,
+        ..,
+        bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb,
+    ) = TupleStruct(1, 2);
+}
+
 // #1095
 struct S<T /* comment */> {
     t: T,